use raw strings for regex to fix backslash interpretation

[ThomasLamprecht]

Fixes these warnings

/usr/share/ifupdown2/ifupdown/utils.py:245: SyntaxWarning: invalid escape sequence '\w'
  range_match = re.match("^([\w]+)\[([\d]+)-([\d]+)\]([\.\w]+)", name)
/usr/share/ifupdown2/ifupdown/utils.py:255: SyntaxWarning: invalid escape sequence '\w'
  range_match = re.match("^([\w\.]+)\[([\d]+)-([\d]+)\]", name)
/usr/share/ifupdown2/ifupdown/ifupdownmain.py:1580: SyntaxWarning: invalid escape sequence '\d'
  vlan_match = re.match("^([\d]+)-([\d]+)", ifacename)
/usr/share/ifupdown2/lib/iproute2.py:65: SyntaxWarning: invalid escape sequence '\s'
  VXLAN_PEER_REGEX_PATTERN = re.compile("\s+dst\s+(\d+.\d+.\d+.\d+)\s+")
/usr/share/ifupdown2/addons/bridge.py:3991: SyntaxWarning: invalid escape sequence '\s'
  for protocol in re.split(',|\s*', user_config_l2protocol_tunnel):